Network nodes may take the form of one or more routers, one or more bridges, one or more switches, one or more servers, or any other suitable communications processing device. The primary function of network nodes is to forward data packets towards their destination. A data packet a formatted unit of data that typically contains control information and payload data. Control information may include information that identifies source addresses, destination addresses, error detection codes like checksums, sequencing information, etc. Control information is typically found in data packet headers and trailers. Payload data is typically located between the headers and trailers.
Operation nodes within a network can be described in terms of a “control plane” and a “data plane.” The data plane, also referred to as the “forwarding plane,” does the actual forwarding of data packets received at a node. Data plane decisions may involve accessing a forwarding table that relates the appropriate control information (e.g., destination address) to the specific network interface, or egress interface, the data packet should be sent to in order to send it in the right direction. Generating such a forwarding table, based on a map, database, or other information reflecting the topology of the network, is a function of the control plane.
The control plane generates and updates its network topology information using one or more routing protocols. An interior gateway protocol (IGP) can be used for exchanging network topology information between nodes. An autonomous system, or routing domain, refers to a collection of interconnected network nodes under a common administration for purposes of network configuration. Exchange of routing information between autonomous systems can be done using an exterior gateway protocol such as Border Gateway Protocol (BGP).